Monomers for photoresists bearing acid-labile groups of reduced optical density

Abstract

Monomers and polymers useful for forming photoresists are provided. More particularly, photoresists, as well as monomers and polymers for photoresists useful in micro-lithography, specifically monomers bearing acid-labile groups of reduced optical density. The resulting photoresists exhibit improved transparency to 157 nm light. The photoresist compositions are composed of a mixture of at least one water insoluble, acid decomposable polymer which is prepared from at least one monomeric unit which comprises an acid labile group of the formula —OC(CH3)2CF3 and which is substantially transparent to ultraviolet radiation at a wavelength of about 157 nm and at least one photoacid generator capable of generating an acid upon exposure to sufficient activating energy at a wavelength of about 157 nm.

Description

BACKGROUND OF THE INVENTION [0001] The invention relates to monomers and polymers useful for forming photoresists. More particularly, the invention pertains to photoresists, as well as monomers and polymers for photoresists useful in micro-lithography, specifically monomers bearing acid-labile groups of reduced optical density. The resulting photoresists exhibit improved transparency to radiation at a wavelength of 157 nm. [0002] Photoresists are organic polymeric materials that are used in a wide variety of applications, including lithographic imaging materials for semiconductor applications, particularly microlithography processes for making miniature electronic components. Generally in these processes a thin film coating of a photoresist composition is applied to a substrate, such as silicon wafers used for making integrated circuits. Any solvent in the photoresist composition is then evaporated to fix the coating onto the substrate. The photoresist coated on the substrate is nex...

AI Technical Summary

Problems solved by technology

However, the resolution capacity that can be obtained with conventional deep UV microlithography has its limits.

However, many photoresist materials that are used today lack transparency at 157 nm, and are therefore not suitable for 157 nm lithography.

The reason why photoresists typically lack transparency at 157 nm is because the high absorbance of many organic functional groups at 157 nm makes it difficult to develop an organic polymer that is both base soluble and has low absorbance at 157 nm.

More specifically, known materials based on phenolic resins as a binding agent, particularly novolak resins or polyhydroxystyrene derivatives have too high an absorption at wavelengths below 200 nm and one cannot image through films of the necessary thickness.

This high absorption, for example at 193 nm radiation, results in side walls of the developed resist structures which do not form the desired vertical profiles.

Rather, they have an oblique angle with the substrate that causes poor optical resolution characteristics at these short wavelengths.

However, while these materials may exhibit transparency to 157 nm radiation, they do not exhibit other desirable properties such as good resistance to plasma etchants, adhesion to a wide range of substances and surfaces and exceptional mechanical properties in 157 nm lithography applications.

However, the precursors used in the preparation of these materials are toxic.

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